An alternative theory for the dynamics of the galaxies, but without dark matter is the modified Newtonian dynamics (MOND),
where Milgrom assumed that the very weak gravitational force experienced by a star in the outer regions
of a galaxy varies inversely linearly with the distance, as opposed
to the inverse square of the distance in Newton's law of gravity [1]}.
Merging galaxies with MOND and with galaxies embedded in
dark matter shows differences in the merging time-scales, but only very small differences in
the final stellar distribution [2]}. The
MOND simulations techniques for modified gravity is given in [3]}. The MOND
theory is extensively tested and compared with
the Lambda cold dark matter model \(\rm {\Lambda }\) CDM and in
favour of the MOND theory [4]}, [5]}.
